Antioxidant for the aqueous solutions of sulfite and/or bisulfite of sodium or potassium and process for preventing the oxidation of said aqueous solution

ABSTRACT

An antioxidant for the aqueous solution of sulfite and/or bisulfite of sodium or potassium which comprises at least one compound selected from the group consisting of 1. SUBSTITUTED PHENOLS REPRESENTED BY THE FORMULA:   WHEREIN R is a lower alkyl group and n is an integer from 1 to 5. 2. TRIS (ALKYLPHENYL) PHOSPHATES REPRESENTED BY THE FORMULA:   WHEREIN R1 is an alkyl group having 6-18 carbon atoms. 3. TRIALKYL PHOSPHITES REPRESENTED BY THE FORMULA:

United States Patent [1 1 Kawamoto et al.

[ June 10, 1975 ANTIOXIDANT FOR THE AQUEOUS SOLUTIONS OF SULFITE AND/ORBISULFITE OF SODIUM OR POTASSIUM AND PROCESS FOR PREVENTING THEOXIDATION OF SAID AQUEOUS SOLUTION [75] Inventors: Kensuke Kawamoto;Tomoaki Tsuno; Teruo Namiki, all of Kitakyushu, Japan [73] Assignee:Mitsubishi Chemical Industries Ltd.,

Tokyo, Japan [22] Filed: Sept. 5. 1972 [21] Appl. No.: 286,559

Primary IiraminerOscar R, Vertiz Assistant E.\aminerGregory A. HellerAttorney, Agent, or FirmBierman & Bierman [57] ABSTRACT An antioxidantfor the aqueous solution of sulfite and- /or bisulfite of sodium orpotassium which comprises at least one compound selected from the groupconsisting of l. substituted phenols represented by the formula:

wherein R is a lower alkyl group and n is an integer from 1 to 5. 2.tris (alkylphenyl) phosphates represented by the formula:

tk n- 1 o wherein R is an alkyl group having 6-18 carbon atoms. 3.trialkyl phosphites represented by the formula:

wherein R- is an alkyl group having 8-l8 carbon atoms.

4. glycerin monofatty acid esters represented by the formula:

wherein R is an alkyl group having 8-22 carbon atoms.

and a process for preventing the oxidation of said aqueous solutionwhich comprises employing said antioxidant.

10 Claims, 1 Drawing Figure BACKGROUND OF THE INVENTION 1. Field OfInvention This invention relates to an antioxidant for aqueous solutionsof sodium or potassium sulfite and/or bisulfite and a process forpreventing oxidation and relates more particularly to the antioxidantused to prevent oxidation of such solutions to the sulfate and theprocess for preventing the oxidation of the aqueous solution of saidsalts by employing said antioxidant.

2. Description Of Prior Art In recent years, various methods have beensuggested and used to remove sulfur dioxide from waste gas to minimizeair pollution. One comprises washing waste gas with an aqueous solutionof sodium or potassium hydroxide and thereby absorbing the sulfurdioxide. While this method is an efficient way to desulfurize and hasadvantages such as the high rate of desulfurization and the easy way totreat the solution, sodium sulfate or potassium sulfate are produced bythe oxidation reaction as a large amount of oxygen contained in wastegas dissolves into the absorbing solution in an absorption column. Whensodium or potassium hydroxide absorb sulfur dioxide, it becomes sulfiteand, when fur ther sulfur dioxide is absorbed it is converted into thecorresponding bisulfite. This bisulfite will regenerate sulfite byliberating sulfur dioxide when it is heated and it is possible torecycle it. The reactions for the sodium hydroxide are as follows:

2NaOH S0 Na SO H O (absorption) Na SO S0 H O ZNaHSO (absorption)ZNaI-ISO Na SO S0 H O (regeneration) When oxygen is present in thissystem, sodium sulfate is produced by oxidation of the sulfite orbisulfite. As sodium sulfate cannnot be regenerated, it must be purgedand fresh sodium hydroxide supplied. The reactions are as follows:

Nazsog /2 02 --D Na SO ZNaHSO /2 O Na SO $0 H O Since the amount andcost of sodium hydroxide increases as a result of sodium sulfate beingproduced, methods to prevent oxidation are desirable. Althoughhydroquinone, phenol, ethyleneglycol and the like have been proposed asantioxidants for these sulfites and/or bisulfites, they are noteffective enough.

Accordingly, it is an object of this invention to provide an antioxidantwhich will effectively prevent oxidation of the aqueous solutions ofsodium or potassium sulfites and/or bisulfites.

A further object of this invention is to provide a method for washingwaste gas to remove sulfur dioxide therefrom without producingundesirable sulfates within the absorbent solution.

SUMMARY OF THE INVENTION In practicing the invention there is providedan antioxidant for the aqueous solution of sulfites and/or bisulfites ofsodium or potassium which comprises at least one compound selected fromthe group consisting of 1. substituted phenols represented by theformula:

wherein R is a lower alkyl group and n is an integer of from 1 to 5.

.2. tris (alkylphenyl) phosphatesrepresented by the formula:

wherein R is an alkyl group having 6-18 carbon atoms. 3. trialkylphosphites represented by the formula:

wherein R is an alkyl group having 8-18 carbon atoms. 4. glycerinmonofatty acid esters represented by the formula:

wherein R is an alkyl group having 8-22 carbon'atoms.

Examples of the alkyl group represented by R are lower alkyl groups suchas methyl, ethyl, butyl, propyl, etc. Examples of the alkyl grouprepresented by R are hexyl, octyl, nonyl, dodecyl, tetradecyl,hexadecyl, octadecyl, and the like. Examples of the alkyl grouprepresented by R are octyl, nonyl, dodecyl, tetradecyl, hexadecyl,octadecyl, and the like. Examples of the alkylv group represented by Rare octyl, nonyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl,eicosyl, docosyl, and the like. These antioxidants may be employedseparately or as a mixture of one or more of them.

The concentration of sulfite and/or bisulfite in aqueous solution is notparticularly limited, but is usually in the range of 5 40% by weightcalculated as sulfite. The amount of antioxidant added to these solutionis in the range of 1-5000 ppm based on the weight of the aqueoussolution and preferably in the range of 10-500 PP Although theantioxidants of this invention may be added as such to the aqueoussulfite and/or bisulfite solutions, usually they are first dissolved inthe appropriate amount of an organic solvent such as alcohols, ethers,ketones, amines, esters, and the like which can dissolve the antioxidantand are water-soluble. Then the solution of antioxidant is added to theaqueous sulfite and/or bisulfite solutions.

In the accompanying drawing constituting a part hereof, the FIGURE showsthe rate at which sodium sulfate is formed when air at 3 liters/min. isblown through ml. of aqueous solutions of various ratios of sodiumsulfite to bisulfite.

In the FIGURE, curve A is a control wherein no antioxidant is used.Curve B shows the use of 50ppm (based on the mixed aqueous solution) ofhydroquinone, the antioxidant of the prior art. Curves C, to C use theantioxidants of this invention at a concentration of 50 ppm. Thesecurves set forth the results of No. 1 of Example 1, No.1 of Example 2,No. 6 of Example 1, and No. 2 of Example 2 respectively. The FIGUREshows that when the antioxidants of this invention are used, the rate offormation of sodium sulfate is slow and it is clear that theantioxidative action is especially good. As is apparent from curve A,the oxidizing speed is greatly influenced by changes in the ratio ofsodium sulfite to sodium bisulfite in the solution.

In the practical case of the absorption of sulfur dioxide, it appearsthat the rate of formation of sodium sulfate changed along with thequick change of the composition of absorbent solution in the absorptioncolumn. Accordingly, an antioxidant is desired which can control therate of formation of sodium sulfate even when the composition of theabsorbent solution changes.

On the other hand, the antioxidants of the present invention do not havethese disadvantages. Compounds like hydroquinone change to quinone whenthey come in contact with oxygen as, for example, by the reaction Theaqueous solution of sulfite and/or bisulfite of sodium or potassiumwhich absorbed sulfur dioxide can be recycled and regenerated byevaporation. However, since the quinones liberate oxygen during thisevaporating process, the amount of sodium sulfate produced increasesmore than if no antioxidant is added. However, when the antioxidants ofthis invention are used,

there is no oxidation during regeneration and the production of sodiumsulfate is prevented.

BRIEF DESCRIPTION OF THE DRAWING The attached FIGURE discloses theantioxidative effect of the antioxidant of this invention. The curves Cto C are the results of the use of the antioxidants of this invention.Curve A is the control using no antioxidant, and curve B is the resultof the use of hydroquinone, the antioxidant of the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the examples, and parts meanweight and parts by weight.

EXAMPLE 1 The antioxidant shown was dissolved in the indicated organicsolvent and was added to 200 parts of an aqueous solution of 13% Na SO2% NaHSO and water. The solution was then aerated at the rate of 3liters/min. The results are shown in Table 1.

Table 1 Styrenated Styrenated phenol phenol n antioxidant kind l l 3 a aMixture of about Mixture of about n=1 of the 15%, n=1 Z of above andabout the above and 10%, n=2 5 85%, n=3 5 of the above. of the above.quantity (parts) 0.01 0.01

ki d acetone acetone solvent quantity (parts) 1 1 0 04 solution quantityprepared (parts) 200 200 solution quantity after aeration (parts) 198197 Na SO 12.75 12.63 anal zed NaHSO 1.92 1.95 resu t Na SQ, 0.41 0.45H2O 84.92 84.97

Tris (hexylphenyl) Tris Trioctyl Tridecyl phosphate (octadecylphenyl)phosphite phosphite l-I phosphate C' 8H3 s 11 )a P 1o 2i )a P -o-) P0O-) PO 0.01; 0.03 0.01 0.01 acetone benzene acetone acetone 6 Table 1Continued 7 Trioctadecyl Glycerin I Glycerin without phospitemonononanate monotricosanate antioxidant (CWHWOL, P C H, .COOCH .CH.CHOH C22H45.COOCH2.C[:.C

OH O

0.02 0.01 0.03 acetone benzene benzene 0.04 0.05 0.15 200 200 200 197197 198 EXAMPLE 2 Table 3 A premixed solution of 0.01 parts of tris(nonylphenyl) phosphate or glycerin monostearate and 0.01 w'th-dmoxldamunnoxldum parts of acetone is added as an antioxidant to 200 parts 20K2303 .7 6.53 of aqueous solution composed of 17% Na SO 51% g- NaHSO0.5%, Na SO and 67.5% water. The solution 20 7 :5 77:95

is then aerated for 3 hours at the rate of 3 liters/min. The analysis ofthe resulting 196 parts of aqueous solution is shown in Table 2. Forcomparison, the results In the above Case, 2 the Waste gas fromCombuswhen no antioxidant is used are also set forth. tion of heavy onafter aeration is 300 PP Table 2 antioxidant No. 1 NO. 2 NO. 3

Tris Glycerin without analyzing (nonylphenyl) monostearate antioxidantitems phosphate C H;, .COOCH .CP.CH OH OH -o-) PO 1421,80 16.75 16.9315.50 NaHSO 14.90 14.85 14.66 M 50. 0.89 0.68 2.63 H O 67.46 67.54 67.21

EXAMPLE 3 What is claimed is:

1. A composition for the absorption of sulfur dioxide which comprisesantioxidant and aqueous solutions of sodium or potassium sulfite orbisulfite or mixtures 50 thereof, said antioxidant being taken from theclass consisting of 0 t} Mixture f about 1. substituted phenolsrepresented by the formula:

If 3 n=1 of this and about 0 f 107.. n=2 5 of this C 7' 1, n

as an antioxidant is added to 600 parts of aqueous solution composed of21% K 5% KHSO and 74% water. The phenol was about wherein n=1 and about10% where n=2 to 5. Waste gas from combustion of heavy oil andcontaining 0.3 vol S0 was aerated for 5 hours at the rate of 15liters/min. The analysis of the 65 resulting 573 parts of aqueoussolution is shown in Table 3. For comparison, the results of the control1 0 PO (without adding antioxidant) are also set forth. 3

A premixed solution of 0.05 parts of acetone and 0.05 parts ofStyrenated phenol wherein R is a lower alkyl group and n is an integerof from 1 to 5 2. tris (alkylphenyl) phosphates represented by theformula:

wherein R is an alkyl group having 8-18 carbom atoms 4. glycerinmonofatty acid esters represented by the formula:

R COOCH CH(OH)CH OH wherein R is an alkyl group having 8-22 carbon atomssaid antioxidant being present in an amount of l to wherein R is a loweralkyl group and n is an integer of from 1 to 2. tris (alkylphenyl)phosphates represented by the formula:

y 8 wherein R is an alkyl group having 6- l8 carbon atoms v 3. trialkylphosphites represented by the formula:

wherein R is an alkyl group having 8-18 carbon atoms 4. glycerinmonofatty acid esters represented by the formula:

R COOCH CH(OH )CH Ol-l wherein R is an alkyl group having 8-22 "carbonatoms.

3. The method according to claim 2 wherein said solutions contain 5 to40% by weight calculated as sulfite of said sulfite and/or bisulfite.

' 4. The method according to claim 2 in which said amount is 10 500 ppm.I

5. The method according to claim 2 comprising first dissolving saidantioxidant in a water soluble organic solvent which is also a solventfor said antioxidant and then adding said antioxidant-solvent to saidsolutions.

6. The method according to claim 2 wherein said solvent is taken fromthe class consisting of alcohols, ethers, ketones, amines and esters.

7. A composition according to claim 1 in which "tris (nonylphenyl)phosphate is employed as the antioxidant.

8. The method according to claim 2 in which tris (nonylphenyl) phosphateis-employed as antioxidant. 9. The method according to claim 2 in whichsaid antioxidant is tris (nonylphenyl) phosphate.

10. The method of claim 2 in which the antioxidant is glycerinemonostearate.

1. SUBSTITUTED PHENOLS REPRESENTED BY FORMULA:
 1. A COMPOSITION FOR THEABSORPTION OF SULFUR DIOXIDE WHICH COMPRISES ANTIOXIDANT AND AQUEOUSSOLUTIONS OF SODIUM OR POTASSIUM SULFITE OR BISULFITE OR MIXTURESTHEREOF, SAID ANTIOXIDANT BEING TAKEN FROM THE CLASS CONSISTING OF 1.SUBSTITUTED PHENOLS REPRESENTED BY THE FORMULA:
 2. TRIS(ALKYLPHENYL)PHOSPHATES REPRESENTED BY THE FORMULA:
 2. TRIS(ALKYLPHENYL) PHOSPHATES REPRESENTED BY THE FORMULA:
 2. THE METHOD FORABSORBING AND REMOVING SULFUR DIOXIDE FROM WASTE GAS WHICH COMPRISESCONTACTING WASTE GAS CONTAINING SULFUR DIOXIDE WITH A COMPOSITIONCONTAINING AQUEOUS SOLUTIONS OF SODIUM OR POTASSIUM SULFITE OR BISULFITEOR MIXTURES THEREOF AND 1 TO 5000 PPM BASED ON THE WEIGHT OF SAIDSOLUTIONS OF AN ANTIOXIDANT TAKEN FROM THE CLASS CONSISTING OF
 3. Themethod according to claim 2 wherein said solutions contain 5 to 40% byweight calculated as sulfite of said sulfite and/or bisulfite. 3.TRIALKYL PHOSPHITES REPRESENTED BY THE FORMULA:
 3. TRICKLY PHOSPHITESREPRESENTED BY THE FORMULA:
 3. trialkyl phosphites represented by theformula: (R1 - O - )3 P wherein R2 is an alkyl group having 8-18 carbomatoms
 3. trialkyl phosphites represented by the formula: (R2 - O - )3 Pwherein R2 is an alkyl group having 8-18 carbon atoms
 4. glycerinmonofatty acid esters represented by the formula: R3 COOCH2CH(OH)CH2OHwherein R3 is an alkyl group having 8-22 carbon atoms.
 4. glycerinmonofatty acid esters represented by the formula: R3 COOCH2CH(OH)CH2OHwherein R3 is an alkyl group having 8-22 carbon atoms said antioxidantbeing present in an amount of 1 to 5000 ppm based on the weight of saidsolutions.
 4. GLYCERIN MONOFATTY ACID ESTERS REPRESENTED BY THE FORMULA:4. GLYCERIN MONOFATTY ACID ESTERS REPRESENTED BY THE FORMULA: R3COOCH2CH(OH)CH2OH AP@ WHEREIN R3 IS AN ALKYL GROUP HAVING 8-22 CARBONATOMS.
 4. The method according to claim 2 in which said amount is 10-500 ppm.
 5. The method according to claim 2 comprising first dissolvingsaid antioxidant in a water soluble organic solvent which is also asolvent for said antioxidant and then adding said antioxidant-solvent tosaid solutions.
 6. The method according to claim 2 wherein said solventis taken from the class consisting of alcohols, ethers, ketones, aminesand esters.
 7. A composition according to claim 1 in which tris(nonylphenyl) phosphate is employed as the antioxidant.
 8. The methodaccording to claim 2 in which tris (nonylphenyl) phosphate is employedas antioxidant.
 9. The method according to claim 2 in which saidantioxidant is tris (nonylphenyl) phosphate.
 10. The method of claim 2in which the antioxidant is glycerine monostearate.